In the canning of food products it has been customary to heat food products in sealed cans in order to sterilize the food products and thereby render microorganisms and their spores such as C.botulinum and B.stearothermophilus, non viable. Various types of food products are processed in this manner, typical of which are vegetables like corn, peas, green beans and cream style corn. In the processing of such foods it is oftentimes important to reduce heat input as much as possible in order to minimize food quality deterioration and at the same time provide enough heat input to ensure commercial sterility. Cream style corn is susceptible to heat degradation (e.g. caramelization) and is viscous compared to the brine used for vegetables like peas, green beans and corn. Head space, i.e. the gas containing portion of the sealed container, is provided in the container to help achieve mixing of the food product within the can during rotation of the can to help improve heat transfer to the entirety of the product so that the entirety of the product will reach the desired sterilization temperature for the required period of time.
A widely used sterilization machine is a continuous sterilizer such as the Sterilmatic manufactured by FMC. Such a sterilizer accomplishes a quick heating of the food product by providing heat to the containers during axial rotation of the cans.
Surprisingly, it was found that even very minor changes in a container, for example a change in the finish and the type of source of container ends, etc., can drastically affect the rotation of the cans in a given piece of processing equipment even though the contents and the processing equipment are unchanged. It has been assumed, until the present invention, that can rotation did not appreciably change due to these factors. Experimental data as disclosed herein, substantiates these effects. It has further been found that the same rotation performance is not guaranteed when changing sterilizers, even if all variables are apparently equal. Thus, the present invention is a means of achieving what has been assumed to be achieved but was not achieved to the desired level of confidence and reliability. That is, the present invention helps assure the required degree of can rotation and hence product heating.
Axial rotation of cans such as metal cans containing foods is a very effective means of increasing the rate of heat transfer to the contained food product. A discussion of this is found in an article entitled "Heat Processing of Viscous Materials in Axially Rotating Cans", an engineering model by E. Rotstein, I. Saguy and K. Valentas, published in Proceedings of the International Symposium on Progress and Food Preservation Processes, Brussels, Belgium, 1:41-50, Apr. 12-14, 1988, the entire disclosure of which is incorporated herein by reference. With viscous food material such as cream style corn it was observed that the actual rotation rate of the cans is extremely important in order to balance the heating time or, more accurately, the heat input into the product in order to assure microorganism kill without unnecessary degradation of the food product. It was found by use of the present invention that heretofore believed to be unimportant factors can materially affect heating of the food products. For example, cans which differ in material or finish may rotate differently even when the processing equipment, rotation rate and the food product and its weight remain unchanged. It has been further found that cans with the same material and finish can rotate differently in different sterilization equipment with the same physical dimensions. It was also determined that within normal processing conditions the product viscosity within an allowable predetermined range, had a much smaller effect than variations in can rotation encountered during operation. Thus, the present invention provides an advance in the processing of canned foods, bringing a higher degree of confidence in the heat processing and sterilization effectiveness.